Historically, liquids such as food, pharmaceuticals, and the like have been filled into containers by means of multiple piston positive displacement pumps. Such systems have various drawbacks. For example, the pumps and pistons have to be mechanically adjusted, are subject to wear, and require substantial time for disassembly to facilitate periodic sterilization and cleaning.
Recently filling machines have emerged with solid state electronics and programmable devices to control the time during which a valve is open which in turn determines fill volume. Those systems are also objectionable in that they require potentially dangerous pressure vessels for containing the supply liquid, require expensive pressure sensing circuits so that the programmable means must take into consideration the pressure in the vessel and/or the speed of a pump. Thus, the last-mentioned systems depend on or seek to maintain constant pressure within the pressure vessel.
The present invention overcomes disadvantages of the prior art by providing a system having the following design criteria:
(a) elimination of all moving parts in contact with the liquid being fed,
(b) elimination of pressure vessels and pressure control systems,
(c) maintain accuracy of fill with pressure variations of 25 percent or more,
(d) facilitate cleaning and sterilization with the use of throw-away components.